Ask Mr. Smarty Plants

Quercus fusiformis (plateau oak) is evergreen, while Quercus muehlenbergii (chinkapin oak), and Quercus shumardii (Shumard's oak) are deciduous. Actually, Live Oaks do drop a third to a half of their leaves, usually in the late winter, every year, but they are smaller and more easily dealt with, plus you have the advantage of the trees being green year-round, which you won't have with the others. All three trees are native to Texas and, therefore, good selections for Austin.

In terms of tree sap, almost all sap falling or dripping from trees is the product of insects, most often aphids. Generally, this aphid damage is not enough to cause problems for cars parked under them. There are other, more serious insect infestations that can cause sap to be exuded. The worst of these does not just cause irritating dribbles on the cars, but can quickly kill the tree. Of the trees you asked about, only Quercus fusiformis (plateau oak) is a live oak. Live Oaks are more susceptible to oak wilt than the others, which should definitely be a consideration in your choice. This link to the Texas Oak Wilt Information Partnership will give you some valuable advice on oak wilt. Please take note of the information on that site, and, if you decide to plant live oaks, to make sure the proper cultural practices are observed in caring for them.

By, the way, all oaks bloom in the spring, and put out a fine dusting of green pollen. Not only is this an allergen for many people, but it's also pretty irritating on paving, walks and cars.

Quercus fusiformis

Quercus muehlenbergii

Quercus shumardii